1. Field of the Invention
The invention relates to an optical device and, in particular, to a tunable optical filter, and a tunable reconfigurable optical add/drop module (TROADM) using the tunable optical filter.
2. Description of the Related Art
The tunable optical filter is an optical device that is often used in an optical fiber system. The tunable optical filter receives multiwavelength optical signals and drops an optical signal having a specific wavelength from the multiwavelength optical signals. In the tunable optical filter, the specific wavelength that is to be dropped is tunable. Tuning a specific wavelength that is to be dropped, the tunable optical filter can drop signals of different channels from the multiwavelength optical signals.
The tunable reconfigurable optical add/drop module (TROADM) utilizes the architecture of the tunable optical filter to drop an optical signal having a specific wavelength from the multiwavelength optical signals. Except for receiving the multiwavelength optical signals, the TROADM further receives a desired optical signal having a specific wavelength, and adds the desired optical signal to the multiwavelength optical signals. Since the tunable optical filter is used, the specific wavelength that is to be added or dropped is tunable. In addition, when adding or dropping an optical signal having a certain specific wavelength, the transmission of other optical signals having other wavelengths is not influenced.
In the prior art, after receiving the multiwavelength optical signals, a TROADM first divides the received multiwavelength optical signals into a number of optical signals having specific wavelengths to travel on different waveguide elements, each of which is connected to a 2xc3x972 optical switch that is used to switch the optical signal to be dropped. Such a TROADM has the following drawbacks. First, the structure of such TROADM is relatively complicated. Second, since a number of filters have to be used to drop an optical signal having a single wavelength, the cost of the TROADM is relatively high and it is difficult to assemble the TROADM.
Another conventional TROADM utilizes Bragg gratings to drop an optical signal having a specific wavelength. By switching between the Bragg gratings having different periods, the TROADM can tune the wavelength that is to be dropped or added. However, except for the need for optical switches, the TROADM still has to use an optical circulator to separate the optical signals input to the Bragg gratings and the optical signals reflected from the Bragg gratings. Using this method still cannot reduce the cost and the difficulties of assembly.
In view of the above-mentioned problems, the invention provides an optical device capable of solving the above-mentioned problems regarding the cost and the difficulties of assembly.
The optical device mainly includes a first input port, a first output port, a second output port, a filter, a reflector, a first reflection unit and a second reflection unit. The filter receives optical signals having wavelengths of xcex1 to xcexn from the first input port. The filter is rotatable to selectively transmit the optical signal having a wavelength of xcexi, and to reflect other optical signals. The first reflection unit reflects the optical signal having the wavelength of xcexi back to the filter, so that the optical signal having the wavelength of xcexi can pass through the filter and be output from the first output port. The reflector reflects the optical signals having the wavelengths of xcex1 to xcexn except for xcexi from the filter. The second reflection unit reflects the optical signals having the wavelengths of xcex1 to xcexn except for xcexi back to the reflector, so that, the optical signals having the wavelengths of xcex1 to xcexn except for xcexi are output from the second output port after being reflected by the reflector and the filter.
The first input port, the first output port, the second output port, the first reflection unit and the second reflection unit are fixed in the optical device. The filter may be a filter film that is optically attached to or plated on a first optical plane of a flat glass, while the reflector may be a reflection film that is optically attached to or plated on a second optical plane of the flat glass. The flat glass is disposed between the first input port and the first reflection unit.
Both of the first reflection unit and the second reflection unit may be right triangular prisms each having two lateral surfaces provided with a reflection film, respectively, to reflect optical signals. Since the shapes of both of the first reflection unit and the second reflection unit are right triangles, the optical path through which the optical signal having the wavelength of xcexi enters the first reflection unit may be parallel to the optical path through which the optical signal having the wavelength of xcexi is reflected. In addition, the optical paths through which the optical signals having wavelength of xcex1 to xcexn except for xcexi enter the second reflection unit may be parallel to the optical paths through which the optical signals having wavelength of xcex1 to xcexn except for xcexi are reflected from the second reflection unit.
By properly designing the sizes of the first reflection unit and the second reflection unit, the distance between the optical path through which the optical signal having the wavelength of xcexi enters the first reflection unit and the optical path through which the optical having the wavelength of xcexi is reflected from the first reflection unit may be substantially equal to that between the first input port and the first output port. Similarly, the distance between the optical path through which the optical signals having the wavelength of xcex1 to xcexn except for xcexi enter the second reflection unit and the optical path through which the optical signals having the wavelength of xcex1 to xcexn except for xcexi are reflected from the second reflection unit may be substantially equal to that between the first input port and the second output port.
The optical device of the invention may further include a second input port for receiving a desired optical signal having a wavelength of xcexi. The desired optical signal can be output therefrom after the desired optical signal passes through the filter and is reflected by the first reflection unit back to the filter.
The optical device of the invention may further include a mirror set, which includes a first mirror, a second mirror and a third mirror. When the mirror set is located between the input port and the reflection unit, the optical signals xcex1 to xcexn from the first input port are reflected to the second output port by the first mirror and the second mirror, while the desired optical signal from the second input port is reflected to the first output port by the first mirror and the third mirror.
Since the numbers of total elements and the movable elements in the optical device of the invention are decreased, the manufacturing cost and the difficulties of assembly can also be decreased.